The primary objective of this proposal is to precisely characterize the breathing pattern of stable but more severe COPD or RLD patients with chronic CO2 retention when NNV is delivered during sleep. A secondary objective is to assess MV using different techniques to evaluate the level of sophistication necessary for equipment to determine whether a net increase in MV actually occurs with NNV. We hypothesize that during an overnight study while using NNV at support pressures of 10-15 cm H2O, at least 50% of these patients will demonstrate an increase in their MV compared to the baseline MV. We further hypothesize that the development of more periodic breathing while using NNV will by itself be a sufficient indicator of augmented MV with sleep as measured by simpler impedance plethysmography methods.